The post mill is entirely made of wood. In Europe it origins in the period 1600-1800. As the rotor-shaft is mounted in the mill-house itself, the whole mill must be turned into the wind, which is done manually from a boom on the backside. With the later Dutch design the rotor-shaft was mounted in a swivelling hat allowing the rotor to change direction independently of the mill-house. The horisontal movement of the hat is automatically performed by a smaller secondary rotor mounted perpendicularly to the main rotor on the backside of the hat. The Dutch construction thereby allowed larger brick-built mill houses.